1. Field of the Invention
This invention relates to highly conductive magnetic particles applications and to a method for preparing such conductive colored magnetic particles, as well as their use in electrostatographic toner compositions.
2. Description of Related Art
Electrostatic charge patterns may be reproduced by means of one of the generally known electrostatographic printing processes, e.g. xerography or by means of a stylus as used for example in a computer printout. The resulting charge pattern may be made visible by means of a toner powder, which by one of the many conventional methods known, is brought into contact with the charge pattern to be developed. These toner powders generally consist of finely divided particles containing a binder and coloring agents.
For some electrostatographic printing applications, it is desirable that the toner powders also contain a magnetic material.
Typical magnetic materials which have appropriate magnetic and electrical properties for use in the preparation of such toner powders include finely divided metal powders of iron, nickel, cobalt, chromium dioxide, gamma ferrioxide and ferrites having a particle size in the range of from about 1 to 50 microns. Many of these materials however exhibit relatively poor electrical conductivity and have an electrical resistivity in the order of 10.sup.5 ohms or greater. Poor electrical conductivity means that mono-component toners containing such particles are not suitable for use in some high speed copy machines which embody a magnetic brush development apparatus.
This problem of poor conductivity of these magnetic materials may be overcome by the addition of highly conductive carbon black to the toner formulation. Such products containing the mixture of magnetic particles and highly conductive carbon black are, however, black in color and consequently the resultant toner compositions are limited for use in the production of black images in the electrostatographic process. Such a toner formulation can not be satisfactorily employed to make colored toner wherein the capability of color highlighting of dark or black images is desired. Neutral colored or matched colored conductive materials which might be added to colored toners to enhance conductivity are not readily available.